Introduction Since the initial (renal angina) RA proposal in 2010 and Developing (renal angina index) RAI, increased in prediction of severe (acute kidney injury) AKI at the time of intensive care unit admission. New biomarkers such as Cystatin C has better performance in prediction of sever AKI in critically ill children with different illness. Aim of the study To test the hypothesis that combination of Cystatin C in patients with renal angina improves the prediction of AKI. Patients and methods In this study 53 critically ill children admitted to the pediatric intensive care unit in our university hospital, Measurement of urine Cystatin C by ELISA kit and in combination with the RAI which is calculated in each critically ill child for severe AKI. Also statistical analysis was done in days (0-3-7). Results Cystatin C has a sensitivity of 76.5%, a specificity of 95%, positive predictive value of 83.3% negative predictive value of 92.7% and accuracy of 90.6% regarding prediction of AKI. Combination of both cystatin C and RAI has a sensitivity of 92.3%, a specificity of 97.5%, positive predictive value of 92.3%, and negative predictive value of 97.5% and accuracy of 96.2% regarding prediction of AKI. Conclusions This study shows that combination of Cystatin C with RAI improves detection ability of AKI in critically ill children.